Apparatus for supplying power source

ABSTRACT

The present invention relates to an apparatus for supplying power source for providing certain voltage to a first display device and a second display device. The apparatus for supplying power source includes a boosting circuit, a boosted voltage detecting circuit and an output selecting circuit. The boosting circuit boosts a battery voltage. The boosted voltage detecting circuit detects the boosted battery voltage, and transmits the detection result to the boosting circuit. The output selecting circuit is coupled to the boosting circuit and the boosted voltage detecting circuit, and provides selectively the boosted battery voltage to a first display device and a second display device. The apparatus provides certain voltage to a first display device and/or a second display device, and thus the size of a dual panel apparatus employing the display devices may be reduced.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for supplying powersource. More particularly, the present invention relates to an apparatusfor supplying power source for providing power source to a first displaydevice and a second display device.

2. Description of the Related Art

An apparatus for supplying power source means apparatus for supplyingpower source required for driving a display device to the displaydevice.

FIG. 1 is a view illustrating circuitry of a common apparatus forsupplying power source.

In FIG. 1, the apparatus for supplying power source 100 includes aboosting circuit 106 and a boosted voltage detecting circuit 108.

The boosting circuit 106 includes a boosting integrated chip 110, aninductor L and a diode D.

The boosting integrated chip 110 boosts a battery voltage outputted froma battery 102, e.g. voltage of 3.7V up to a predetermined voltage, e.g.18V. Accordingly, a first node N1 has the voltage boosted by theboosting circuit 106, and the voltage of the first node N1 is providedto the display device 104.

The boosted voltage detecting circuit 108 detects the battery voltageboosted by the boosting circuit 106, i.e. the voltage of the first nodeN1 and a voltage of a second node N2, and then provides the voltage ofthe second node N2 to a feedback terminal FB of the boosting integratedchip 110. The boosted voltage detecting circuit 106 includes resistorsR1 and R2 and capacitors C1 and C2.

The capacitors C1 and C2 make the voltage of the first node N1 providedto the display device 104 stabilize.

The boosting integrated chip 110 adjusts its boosting rate in accordancewith the voltage of the second node N2 provided from the boosted voltagedetecting circuit 108.

In brief, the apparatus for supplying power source 100 provides apredetermined voltage to only one display device 104.

However, recently, a dual panel apparatus such as a mobile terminal anda laptop, etc. employs two display devices, and thus should include twoapparatuses for supplying power source for driving the display devices.Accordingly, the size of the dual panel apparatus may be increased.

SUMMARY OF THE INVENTION

It is a feature of the present invention to provide an apparatus forsupplying power source for providing power source to a plurality ofdisplay devices.

An apparatus for supplying power source includes a boosting circuit, aboosted voltage detecting circuit and an output selecting circuit. Theboosting circuit boosts a battery voltage. The boosted voltage detectingcircuit detects the boosted battery voltage, and transmits the detectionresult to the boosting circuit. The output selecting circuit is coupledto the boosting circuit and the boosted voltage detecting circuit, andprovides selectively the boosted battery voltage to a first displaydevice and a second display device.

An apparatus for supplying power source according to another embodimentof the present invention includes a boosting circuit, a voltageadjusting circuit and an outputting circuit. The boosting circuit boostsa battery voltage. The voltage adjusting circuit controls the boostingcircuit so that the boosting circuit boosts the battery voltage up to afirst voltage or a second voltage. The outputting circuit provides thefirst voltage to a first display device, downs the second voltage, andprovides the downed second voltage to a second display device.

As described above, the apparatus for supplying power source providescertain voltage to a first display device and/or a second displaydevice, and thus the size of a dual panel apparatus employing thedisplay devices may be reduced.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other features and advantages of the present inventionwill become readily apparent by reference to the following detaileddescription when considered in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a view illustrating circuitry of a common apparatus forsupplying power source;

FIG. 2 is a block diagram illustrating an apparatus for supplying powersource according to one embodiment of the present invention;

FIG. 3 is a view illustrating a circuitry of the apparatus for supplyingpower source of FIG. 2;

FIG. 4 is a block diagram illustrating an apparatus for supplying powersource according to another embodiment of the present invention; and

FIG. 5 is a view illustrating a circuitry of the apparatus for supplyingpower source of FIG. 4 according to one embodiment of the presentinvention.

DESCRIPTION OF EMBODIMENTS

Hereinafter, the preferred embodiments of the present invention will beexplained in more detail with reference to the accompanying drawings.

FIG. 2 is a block diagram illustrating an apparatus for supplying powersource according to one embodiment of the present invention.

In FIG. 2, the apparatus for supplying power source 200 of the presentinvention includes a boosting circuit 208, a boosted voltage detectingcircuit 210 and an output selecting circuit 212.

The boosting circuit 208 boosts a battery voltage outputted from abattery 202 up to a desired voltage. For example, in case that a voltageof 20V is preset to be provided to a first display device 204, theboosting circuit 208 boosts the battery voltage, e.g. voltage of 3.7V upto 20V. For another example, in case that a voltage of 18V is preset tobe provided to a second display device 206, the boosting circuit 208boosts the battery voltage of 3.7V up to 18V.

In one embodiment of the present invention, the first display device 204is liquid crystal display, and the second display device 206 is organicelectroluminescent device.

In another embodiment of the present invention, each of the displaydevices 204 and 206 is organic electroluminescent device.

In still another embodiment of the present invention, the displaydevices 204 and 206 may be employed as display sections of a mobileterminal.

The boosted voltage detecting circuit 210 detects the battery voltageboosted by the boosting circuit 208, and transmits the detection resultto the boosting circuit 208. The boosting circuit 208 analyzes thedetection result transmitted from the boosted voltage detecting circuit210, and adjusts its boosting ratio, e.g. duty ratio in accordance withthe analysis.

For instance, a voltage to be provided to the first display device 204is preset to be 18V.

The boosting circuit 208 boosts the battery voltage, e.g. voltage of3.7V up to a voltage of 17.5V. In this case, the boosted voltagedetecting circuit 210 detects the battery voltage boosted up to 17.5V,and transmits the detection result to the boosting circuit 208.

Subsequently, the boosting circuit 208 detects that the battery voltageis boosted up to 17.5V through the detection result transmitted from theboosted voltage detecting circuit 210, and increases its boosting ratioin order to boost the battery voltage up to 18V. For example, if theboosting circuit 208 boosts the battery voltage by using on/off ratio ofswitch (not shown) included therein, i.e. duty ratio, the boostingcircuit 208 boosts its duty ratio in accordance with the detectionresult transmitted from the boosted voltage detecting circuit 210. Inother words, the boosting circuit 208 boosts the battery voltage up to18V by adjusting its duty ratio.

The apparatus 200 of the present invention boosts the battery voltage upto a desired voltage through the above process.

The output selecting circuit 212 is coupled to the boosting circuit 208and the boosted voltage detecting circuit 210, and provides the batteryvoltage boosted by the boosting circuit 208 to the first display device204 or the second display device 206.

Hereinafter, operation of the output selecting circuit 212 will bedescribed in detail with reference to a mobile terminal.

The mobile terminal employs the first display device 204 as main displaysection, and employs the second display device 206 as sub displaysection.

In case that the mobile terminal is folder-typed terminal and folder ofthe mobile terminal is open, the first display device 204 is turned onand the second display device 206 is turned off. In this case, theoutput selecting circuit 212 of the apparatus 200 of the presentinvention provides the battery voltage boosted by the boosting circuit208 to the first display device 204.

Whereas, in case that the mobile terminal operates under condition ofclosing the folder thereof, the first display device 204 is turned off,and the second display device 206 is turned on. In this case, the outputselecting circuit 212 provides the battery voltage boosted by theboosting circuit 208 to the second display device 206.

On the other hand, the boosting degree of the battery voltage isdetermined by the boosting circuit 208 and the boosted voltage detectingcircuit 210. This will be described in detail with reference toaccompanying drawings.

In short, the apparatus for supplying power source 200 of the presentinvention may provide power source to the first display device 204 orthe second display device 206 unlike the apparatus for supplying powersource described in Related Art. Accordingly, in case that a dual panelapparatus, e.g. mobile terminal employs the apparatus 200 of the presentinvention, the apparatus 200 may supply power supply to the firstdisplay device 204 and the second display device 206. As a result, thesize of the dual panel apparatus may be reduced.

FIG. 3 is a view illustrating a circuitry of the apparatus for supplyingpower source of FIG. 2 according to one embodiment of the presentinvention.

In FIG. 3, the boosting circuit 208 includes a boosting integrated chip220 activated in accordance with a controlling signal provided from afirst signal terminal S1, an inductor L and a diode D.

The boosted voltage detecting circuit 210 is coupled to the boostingcircuit 208, and includes a first resistor R1, a second and thirdresistors R2 and R3, a first switch T1 and capacitors C1 and C2. Here,the resistors R2 and R3 are coupled to the first resistor R1, and arecoupled in parallel each other.

The output selecting circuit 212 includes a second switch T2 and aninverter coupled to the first switch T1, and a third switch T3 coupledin serial to the inverter.

Hereinafter, operation of the apparatus 200 of the present inventionwill be described in detail. Here, the first switch T1 is P-MOStransistor, each of the second and third switches T2 and T3 is N-MOStransistor. In addition, a voltage of 20V is provided to the firstdisplay device 204, and a voltage of 18V is provided to the seconddisplay device 206.

Firstly, the first switch T1 is turned off in accordance with acontrolling signal provided from a second signal terminal S2. In thiscase, the second switch T2 is turned on, and the third switch T3 isturned off. Additionally, the boosted voltage detecting circuit 210 ismade up of resistors R1 and R2 coupled in serial.

When the boosting circuit 208 boosts the battery voltage, the boostedvoltage detecting circuit 210 detects a voltage of the third node N3.For example, when a voltage of the second node N2 is 18V, the voltage ofthe third node N3 is assumed to be 1.5V.

The boosted voltage detecting circuit 210 detects the voltage of thethird node N3, e.g. detects the voltage of the third node N3 of 1.3Vcorresponding to the voltage of the second node N2 of 16V.

Subsequently, the boosted voltage detecting circuit 210 provides thevoltage of the third node N3 of 1.3V to the FB of the boostingintegrated chip 220. As a result, the boosting integrated chip 220detects that the battery voltage is not boosted up to a predeterminedvoltage (18V), and so increases its boosting ratio.

The second node N2 has voltage of 18V through the above process, and thevoltage of the second node N2 is provided to the second display device206.

Secondly, in case that the first switch T1 is turned-on, the secondswitch T2 is turned off, and the third switch T3 is turned-on. Thus, theresistors R2 and R3 coupled in parallel are coupled to the firstresistor R1.

Here, since the second and third resistors R2 and R3 are coupled inparallel each other, a resistance formed by the resistors R2 and R3 issmaller than that of the second resistor R2. As a result, the voltage ofthe third node N3 when the third resistor R3 is coupled to the secondresistor R2 is smaller than that when the third resistor R3 is notcoupled to the second resistor R2. For example, in case that the secondnode N2 has 16V, the voltage of the third node N3 when the thirdresistor R3 is not coupled to the second resistor R2 is 1.3V. Whereas,the voltage of the third node N3 when the third resistor R3 is coupledto the second resistor R2 is 1.2V. Hence, when the third resistor R3 iscoupled to the second resistor R2, the boosting integrated chip 220increases its boosting ratio more than boosting ration when the thirdresistor R3 is not coupled to the second resistor R2, and so the secondnode N2 has 20V higher than 18V. The voltage of 20V is provided to thefirst display device 204.

In short, the apparatus 200 of the present invention providesselectively voltages having different magnitude to the first displaydevice 204 and the second display device 206 by using the first switchT1 and the resistors R2 and R3.

In the apparatus 200 according to anther embodiment of the presentinvention, the boosted voltage detecting circuit 210 may be include atleast three resistors which are coupled to the first resistor R1, andare coupled in parallel one another.

FIG. 4 is a block diagram illustrating an apparatus for supplying powersource according to another embodiment of the present invention.

In FIG. 4, the apparatus for supplying power source 400 of the presentinvention includes a boosting circuit 410, a voltage adjusting circuit412 and an outputting circuit 414.

The boosting circuit 410 boosts a battery voltage outputted from abattery 402 up to a desired voltage.

The voltage adjusting circuit 412 adjusts boosting ratio of the boostingcircuit 410 so that the boosting circuit 410 boosts the battery voltageup to the desired voltage.

The outputting circuit 414 provides the battery voltage boosted by theboosting circuit 410 to a first display device 404 and/or a seconddisplay device 406, and has a switching circuit 416 and a voltage downcircuit 418.

The switching circuit 416 switches couple between the boosting circuit410 and the first display device 404, and provides the battery voltageboosted by the boosting circuit 410 to the first display device 404.

The voltage down circuit 418 downs the battery voltage boosted by theboosting circuit 410, and provides the downed voltage to the seconddisplay device 406.

FIG. 5 is a view illustrating a circuitry of the apparatus for supplyingpower source of FIG. 4 according to one embodiment of the presentinvention.

In FIG. 5, the boosting circuit 410 is made up of a boosting integratedchip 500, an inductor L and a first diode D1.

The boosting integrated chip 500 boosts the battery voltage outputtedfrom the battery 402 using switch (not shown) included therein asdescribed below.

Firstly, the switch is turned off, and so the battery voltage is storedin the inductor L.

Subsequently, the switch is turned on, and so charges charged in theinductor L is outputted to a first node N1.

Then, the switch is turned off, and so the battery voltage is stored inthe inductor L.

Subsequently, the switch is turned on, and so charges charged in theinductor L is outputted to the first node N1.

In other words, the switch is repeatedly turned on/off, and so thebattery voltage is boosted. As a result, the first node N1 has theboosted battery voltage. Here, on/off ratio of the switch means dutyratio.

Then, when the boosted battery voltage is more than threshold voltage ofthe first diode D1, current outputted from the inductor L is provided toa second node N2 through the first diode D1. As a result, the secondnode N2 has the battery voltage boosted by the boosting circuit 410.

Hereinafter, the elements of the apparatus 400 will be continuouslydescribed in detail.

The voltage adjusting circuit 412 includes a first capacitor C1, asecond diode D2, a first resistor R1, a second resistor R2, a thirdresistor R3, a first switch T1, a second switch T2, a second capacitorC2 and a third capacitor C3.

The first capacitor C1 is coupled to the boosting circuit 410, and thesecond diode D2 is coupled to the first capacitor C1 and the boostingintegrated chip 500. The first capacitor C1 and the second diode D2 makea voltage inputted to FB of the boosting integrated chip 500, i.e.voltage of a third node N3 stabilize.

The first resistor R1 is coupled to the boosting circuit 410, and thesecond resistor R2 is selectively coupled to the first resistor R1. Inother words, when the first switch T1 is turned on by a controllingsignal transmitted from a second signal terminal S2, the second resistorR2 is coupled in serial to the first resistor R1. However, when thefirst switch T1 is turned off, the second resistor R2 is not coupled tothe first resistor R1. Accordingly, though the boosting integrated chip500 has the same boosting ratio, voltage outputted from the boostingcircuit 410 may be changed depending on couple of the resistors R1 andR2. Hence, in the apparatus 400 of the present invention, the boostingcircuit 410 may output voltages having different magnitude using thesame boosting ratio.

The third resistor R3 is coupled in parallel to the second resistor R2when the second switch T2 is turned on in accordance with a controllingsignal provided from a third signal terminal S3. In other words, thethird resistor R3 is resistor used for adjusting the boosting ratio ofthe boosting circuit 410.

In the apparatus 400 according to one embodiment of the presentinvention, each of the switches T1 and T2 is MOS transistor, preferablyN-MOS transistor.

In the apparatus 400 according to another embodiment of the presentinvention, a fourth resistor R4 may be coupled between a gate terminalof the first transistor T1 and a ground in order to protect the firsttransistor T1. In addition, a fifth resistor R5 may be coupled between agate terminal of the second transistor T2 and the ground so as toprotect the second transistor T2.

The second and third capacitors C2 and C3 make voltage provided to thedisplay devices 404 and 406, i.e. voltage of the second node N2stabilize.

The switching circuit 416 includes a third switch T3, e.g. MOStransistor switching in accordance with a controlling signal transmittedfrom a fourth signal terminal S4.

The voltage down circuit 418 includes an LDO (Low DropOut) regulator 502for downing the voltage outputted from the boosting circuit 410, aseventh resistor R7 coupled between a ground terminal GND and an outputvoltage adjusting terminal ADJ of the LDO regulator 502, and an eighthresistor R8 coupled between the ADJ and the second display device 406.

The voltage down circuit 418 adjusts the voltage outputted from theboosting circuit 410 inputted to a voltage input terminal VIN of the LDOregulator 502 using the resistors R7 and R8 coupled to the ADJ of theLDO regulator 502. In particular, the LDO regulator 502 is turned on inaccordance with a controlling signal transmitted from a fifth signalterminal S5 coupled to an enable terminal EN of the LDO regulator 502,and then the voltage outputted from the boosting circuit 410 is inputtedto the LDO regulator 502. As a result, the LDO regulator 502 downs thevoltage outputted from the boosting circuit 410 to a desired voltage inaccordance with the resistors R7 and R8.

In addition, the voltage down circuit 418 may further include a sixthresistor R6 and a fourth capacitor C4.

The sixth resistor R6 as full down resistor is coupled between the ENand the ground terminal GND of the LDO regulator 502, and stabilizes adigital signal inputted to the ground terminal GND of the LDO regulator502.

The fourth capacitor C4 stabilizes a voltage outputted from the LDOregulator 502 provided to the second display device 406.

Hereinafter, operation of the apparatus 400 of the present inventionwill be described in detail.

In a first embodiment, the switching circuit 416 is turned on, and theLDO regulator 502 is not activated in accordance with a controllingsignal transmitted from the fifth signal terminal S5. Additionally, whenthe battery voltage, e.g. voltage of 3.7V is boosted up to 20V, thethird node N3 is assumed to have 9V.

In this case, the first switch T1 and the second switch T2 are turnedon. Here, in case that the battery voltage boosted by the boostingcircuit 410 is 16V, the voltage adjusting circuit 412 detects that thevoltage of the third node N3 is 7V in accordance with distribution ofthe resistors R1 to R3.

Subsequently, the voltage adjusting circuit 412 provides the detectedvoltage of the third node N3 to the FB of the boosting integrated chip500.

In this case, the boosting integrated chip 500 detects that the batteryvoltage is not boosted up to a desired voltage (20V) through thedetected voltage of the third node N3 provided from the voltageadjusting circuit 412. Accordingly, the boosting integrated chip 500boosts the battery voltage up to the desired voltage (20V) by adjustingits duty ratio. Here, the boosted battery voltage of 20V is provided tothe first display device 404 through the switching circuit 416.

In a second embodiment, the switching circuit 416 is turned off, and theLDO regulator 502 is activated in accordance with a controlling signaltransmitted from the fifth signal terminal S5. Additionally, when thebattery voltage, e.g. voltage of 3.7V is boosted up to 18V, the thirdnode N3 is assumed to have 9V.

In this case, the first switch T1 is turned on, and the second switch T2are turned off. Here, in case that the battery voltage boosted by theboosting circuit 410 is 16V, the voltage adjusting circuit 412 detectsthat the voltage of the third node N3 is 8V in accordance withdistribution of the resistors R1 and R2.

Subsequently, the voltage adjusting circuit 412 provides the detectedvoltage of the third node N3 to the FB of the boosting integrated chip500.

In this case, the boosting integrated chip 500 detects that the batteryvoltage is not boosted up to a desired voltage (18V) through the voltageof the third node N3 provided from the voltage adjusting circuit 412.Accordingly, the boosting integrated chip 500 boosts the battery voltageup to the desired voltage (18V) by adjusting its duty ratio. Here, theboosted battery voltage of 18V is downed by the voltage down circuit418, and then the downed voltage is provided to the second displaydevice 406.

Hereinafter, a method in the first embodiment and a method in the secondembodiment will be compared.

In the first embodiment, since the first and second switches T1 and T2are turned on, the resistors R2 and R3 are coupled in parallel eachother. However, in the second embodiment, since the first switch T1 isturned on and the second switch T2 is turned off, only the secondresistor R2 of the resistors R2 and R3 is activated. Therefore, when thebattery voltage boosted by the boosting circuit 410 is 16V, the thirdnode N3 has 7V in the first embodiment, but has 8V in the secondembodiment. As a result, the battery voltage boosted by the boostingcircuit 410 is 20V in the first embodiment, but is 18V in the secondembodiment. Accordingly, the boosted battery voltage of 20V is providedto the first display device 404. In addition, the boosted batteryvoltage of 18V is downed by the voltage down circuit 418, and then thedowned voltage is provided to the second display device 406.

In the second embodiment, if the second switch T2 is turned on like thefirst embodiment, the boosted battery voltage is 20V. Then, the boostedbattery voltage of 20V is downed by the voltage adjusting circuit 418,and the downed voltage is provided to the second display device 406.

Accordingly, in the second embodiment, power consumption of theapparatus 400 when the second switch T2 is turned on is higher than thatof the apparatus 400 when the second switch T2 is turned off. Hence, inthe second embodiment, the second switch T2 is turned off, and so powerconsumption of the apparatus 400 may be reduced.

In brief, the apparatus 400 of the present invention reduces its powerconsumption by properly combining the resistors R1 to R3. For example,in case that the first display device 404 is main display section of adual panel apparatus, a first voltage is provided to the first displaydevice 400. However, in case that the second display device 406 is subdisplay section of the dual panel apparatus, a second voltage smallerthan the first voltage is downed so as to enhance power consumption ofthe apparatus 400, and then the downed voltage is provided to the seconddisplay device 406.

In a third embodiment, the switching circuit 416 is turned on, and theLDO regulator 502 is activated in accordance with a controlling signaltransmitted from the fifth signal terminal S5.

In this case, the battery voltage boosted by the boosting circuit 410,e.g. voltage of 20V is provided to the first display device 404.Additionally, the boosted battery voltage of 20V is downed by thevoltage down circuit 418, and then the downed voltage is provided to thesecond display device 406.

In short, the apparatus for supplying power source 400 of the presentinvention may provide corresponding power source to the first displaydevice 404 and/or the second display device 406 of the dual panelapparatus.

From the preferred embodiments for the present invention, it is notedthat modifications and variations can be made by a person skilled in theart in light of the above teachings. Therefore, it should be understoodthat changes may be made for a particular embodiment of the presentinvention within the scope and the spirit of the present inventionoutlined by the appended claims.

1. An apparatus for supplying power source comprising: a boostingcircuit configured to boost a battery voltage; a boosted voltagedetecting circuit configured to detect the boosted battery voltage, andtransmit the detection result to the boosting circuit; and an outputselecting circuit coupled to the boosting circuit and the boostedvoltage detecting circuit, and configured to provide selectively theboosted battery voltage to a first display device and a second displaydevice.
 2. The apparatus of claim 1, wherein the boosted voltagedetecting circuit includes a first resistor, and a second resistor and athird resistor coupled to the first resistor, wherein the second andthird resistors are coupled in parallel each other.
 3. The apparatus ofclaim 2, wherein the boosted voltage detecting circuit further includesa first switch coupled to the third resistor.
 4. The apparatus of claim3, wherein the output selecting circuit includes a second switch and athird switch coupled to the first switch.
 5. The apparatus of claim 4,wherein at least one of the switches are MOS transistor.
 6. Theapparatus of claim 3, wherein the output selecting circuit includes asecond switch and an inverter coupled to the first switch, and a thirdswitch coupled to the inverter, wherein the second switch and theinverter are coupled in parallel each other.
 7. The apparatus of claim3, wherein the first switch is P-MOS transistor.
 8. The apparatus ofclaim 1, wherein the first display device is a first display section ofa dual panel apparatus, and the second display device is a seconddisplay section of the dual panel apparatus.
 9. The apparatus of claim8, wherein the first display device is liquid crystal display, and thesecond display device is organic electroluminescent device.
 10. Anapparatus for supplying power source comprising: a boosting circuitconfigured to boost a battery voltage; a voltage adjusting circuitconfigured to control the boosting circuit so that the boosting circuitboosts the battery voltage up to a first voltage or a second voltage;and an outputting circuit configured to provide the first voltage to afirst display device, down the second voltage, and provide the downedsecond voltage to a second display device.
 11. The apparatus of claim10, wherein the second voltage is substantially identical to the firstvoltage.
 12. The apparatus of claim 10, wherein the second voltage hasdifferent magnitude from the first voltage.
 13. The apparatus of claim10, wherein the outputting circuit includes: a switching circuitconfigured to switch couple between the boosting circuit and the firstdisplay device; and a voltage down circuit configured to down the secondvoltage outputted from the boosting circuit, and provide the down secondvoltage to the second display device.
 14. The apparatus of claim 13,wherein the switching circuit includes MOS transistor.
 15. The apparatusof claim 13, wherein the second voltage is smaller than the firstvoltage.
 16. The apparatus of claim 13, wherein the voltage down circuitincludes: an LDO regulator coupled between the boosting circuit and thesecond display device; resistors R6 and R7 coupled in parallel to aground terminal GND of the LDO regulator; and a resistor R8 coupled toan output terminal VOUT of the LDO regulator.
 17. The apparatus of claim10, wherein the boosting circuit includes: a boosting integrated chipconfigured to boost the battery voltage; an inductor coupled to theboosting integrated chip; and a diode D1 coupled to the inductor. 18.The apparatus of claim 17, wherein the voltage adjusting circuitcontrols the boosting circuit using a plurality of resistors.
 19. Theapparatus of claim 17, wherein the voltage adjusting circuit includes:resistors R1 to R3 coupled in parallel to a feedback terminal FB of theboosting integrated chip.
 20. The apparatus of claim 19, wherein thevoltage adjusting circuit further includes: a first switch configured toswitch couple between a second resistor R2 of the resistors R1 to R3 anda ground; and a second switch configured to switch couple between athird resistor R3 of the resistors R1 to R3 and the ground.
 21. Theapparatus of claim 20, wherein at least one of the switches is made upof MOS transistor.
 22. The apparatus of claim 10, further comprising: abattery configured to provide the battery voltage to the boostingcircuit.
 23. The apparatus of claim 10, wherein one or more of the firstdisplay device and the second display device is organicelectroluminescent device.
 24. The apparatus of claim 10, wherein thefirst display device is main display section of a dual panel apparatus,and the second display device is sub display section of the dual panelapparatus.